The project studies
the effects of heavy metal pollution on the structure and
functioning of a belowground foodweb. Research area Detritivores Research until now: Future research: Duration: 4 years Participants:
The research area consists of tidal floodplains in the
Biesbosch, the Netherlands, with a dominant vegetation of
stinging nettle (Urtica dioica) and common reed
(Phragmites australis). The Biesbosch is the delta of
the rivers Rhine and Meuse. Pollution of these rivers with
heavy metals started early in the 19th century
and was highest during the 1960's and 1970's. After this
period metal levels in the water decreased again as a result
of environmental policy. Deposition of polluted particles
was also reduced by the building of the Haringvlietdam in
1970, which decreased the frequency of flooding of Biesbosch
flood plains. However, total soil concentrations of heavy
metals remained high as a result of sedimentation of
polluted particles and binding of heavy metals to soil
particles during the period of water pollution.
The project focuses on detritivores (e.g., earthworms,
isopods and millipedes), because they play an important role
in the decomposition of litter. They fragmentate litter
which increases the surface area exposed to bacteria and
fungi and also inoculate litter with bacteria and fungi
during passage through their gut. Earthworms are also
important 'ecosystem engineers'. By making burrows in the
soil they change the moisture content and mix the organic
and mineral layer. Therefore, negative effects of heavy
metals on detritivores possibly influence the decomposition
of litter and therefore the functioning of
ecosystems.
Two heavily polluted sites in the Biesbosch were
inventarised to determine the structure of the detritivore
community. The possible effects of heavy metals on the
functioning of these detritivores were assessed by measuring
the internal concentrations of heavy metals in detritivores
and comparing them to internal concentrations found in
unpolluted reference areas. Results show that there is a
possible effect of heavy metals on the functioning of
earthworms, but not on the functioning of isopods and
millipedes.
With reference to the previous results, the project
focuses on the effects of heavy metal pollution on
earthworms. The influence of heavy metals on the food
consumption and burrowing behaviour of earthworms will be
studied in laboratory experiments because these variables
are related to functioning of earthworms in the
decomposition processes and to their functioning as
ecosystem engineers. It will also be studied if the Dynamic
Energy Budget model of Bas Kooijman (www.bio.vu.nl/thb/deb)
can be used to model the relation between food consumption,
internal concentration of heavy metals and energy demanding
processes like maintenance, growth and reproduction.